Currently, a mainstream display (Display) is also referred to as a display panel. There are two main types of displays: a liquid crystal display (Liquid-Crystal Display, LCD) and an organic light-emitting diode (organic light-emitting diode, OLED) display. FIG. 1 is a schematic structural diagram of an LCD display and an OLED display. The LCD display includes a backlight unit (Back Light Unit, BLU) 132, a bottom polarizer 134, a thin-film transistor (Thin-Film Transistor, TFT) glass layer 136, a liquid crystal layer 138, a color filter (Color Filter, CF) 140, and a top polarizer 142. A structure of the OLED display includes a TFT glass substrate 150, an OLED layer 152, a package glass 154, and a polarizer 156.
For a detailed description about the OLED display, refer to a webpage of Wikipedia: https://en.wikipedia.org/wiki/OLED (last access time is Jun. 27, 2016). For a detailed description about the LCD display, refer to a webpage of Wikipedia: https://en.wikipedia.org/wiki/Liquid-crystal display (last access time is Jun. 27, 2016).
Currently, many displays further include a touch control layer, and accordingly, this touchable display is referred to as a touchscreen.
To improve interaction between human and a terminal device such as a mobile phone, a watch, or a wearable device, currently, a pressure sensor is widely applied to parts of the terminal device such as a touchscreen and a housing, so as to identify touch pressure of the user as well as a touch position of the user. Therefore, operation experience with richer content is implemented. A capacitive pressure sensor of Apple company is used as an example. A screen of the mobile phone product iPhone 6s of Apple company is an LCD display. FIG. 2 is a schematic diagram of an iPhone with a pressure (force) sensing function. Herein, 102 is a cover glass (Cover Glass, CG) of the mobile phone, 104 is a display, and 110 is an iron frame of the mobile phone. There is an extremely thin air gap (air gap) between the display 104 and the iron frame 110. A specific structure of the display 104 may be the LCD display structure shown in FIG. 1.
A basic principle of the capacitive pressure sensor of Apple company is as follows: A first electrode 106 is disposed below the display 104, and a second electrode 108 is disposed above a middle frame (not shown in the figure) or the iron frame 110 of the mobile phone. The first electrode 106, the second electrode 108, and the air gap between the first electrode 106 and the second electrode 108 jointly form a capacitor C. An equivalent circuit of the capacitor C is shown in FIG. 3(1). The air gap is used as a dielectric of the capacitor C. When the user presses the screen, because there is the air gap between the display 104 and the iron frame 110, a small deformation is caused to the screen in a pressing direction of the user. As shown in FIG. 3(2), the small deformation causes a change of a capacitance value of the capacitor C, and a variation of the capacitance value is directly proportional to a value of pressure. That is, the variation of the capacitance value may be detected, to detect the value of the pressure. However, the capacitive pressure sensor detects the pressure on the display mainly according to a change of a distance between the dioxides. Therefore, the distance between the dioxides needs to be large enough to ensure accuracy. This increases an overall thickness of the terminal device.
In addition, bottom stacked layers of the OLED display are the TFT and the OLED. The TFT and the OLED are relatively fragile, and have a poor impact resistance capability. Therefore, when the OLED display is applied to the terminal device, a thin foam layer is disposed at the bottom of the OLED display, to mitigate an impact. The foregoing solution of the capacitive pressure sensor is not applicable to the OLED display due to the foam.